Anembryonic pregnancy (blighted ovum): what it is and why it happens
What an anembryonic pregnancy is, why it happens, what the signs are, how it is diagnosed on ultrasound and which options exist afterwards.
Early pregnancy is an exciting time, but it also carries its share of uncertainty. One of the situations that causes the most worry in the first weeks — and one seen fairly often in practice — is what is commonly called an "empty pregnancy".
Its medical name is anembryonic pregnancy, and it accounts for a substantial share of early pregnancy losses. What follows sets out what it is, where it comes from, and how diagnosis and recovery usually go.
What is an anembryonic pregnancy?
In a pregnancy that is developing normally, the fertilised egg implants in the wall of the womb, and from there both the gestational sac and the embryo grow at the same time.
In an anembryonic pregnancy, the fertilised egg does implant and a gestational sac does form, but no embryo develops inside that sac — or its development stops at a very early stage. The sac keeps growing and pregnancy hormones keep being produced, but the sac is empty. In medical terms this is a form of early miscarriage.
Why does it happen?
An anembryonic pregnancy is not caused by anything the mother or father did, by diet, or by physical activity such as lifting something heavy. The research points to two things:
- Chromosomal abnormalities: during fertilisation, the genetic material in the sperm or the egg pairs incorrectly as the cells divide.
- Natural selection: the body recognises early on that this structure cannot develop in a genetically healthy way, and development stops. This is an entirely natural mechanism in human reproduction.
What are the signs?
At first, an anembryonic pregnancy gives exactly the same signals as a healthy one. That is because, even without an embryo, the gestational sac — and the cells that would later form the placenta — carries on producing beta-hCG, the pregnancy hormone.
- Early signs: a missed period, a positive pregnancy test, breast tenderness and mild nausea — the classic signs of pregnancy.
- Warning signs later on: once the body registers that the pregnancy is not progressing and prepares to pass the sac, brown spotting, light to moderate vaginal bleeding and period-like cramps in the lower abdomen may begin. In some women there are no signs at all, and the situation is picked up only at a routine ultrasound.
How is it diagnosed?
The diagnosis can only be made by a doctor, on ultrasound.
- On a transvaginal or abdominal scan, the diagnosis is made when the gestational sac has reached a certain diameter (generally 25 mm or more) but neither a yolk sac nor any embryonic structure — a heartbeat — can be seen inside it.
- If the pregnancy is still very early (5-6 weeks, say), your doctor may suggest repeating the scan after 7 to 10 days, so that late ovulation is ruled out before anything is concluded.
What happens next?
Once the diagnosis is confirmed, the gestational sac needs to be cleared from the womb. There are three broad approaches, chosen according to the clinical picture and the woman's own preference:
- Waiting (expectant management): where there is no sign of infection and heavy bleeding is not a concern, it is possible to wait a short while for the body to pass the sac on its own.
- Medical management: under medical supervision, medicines can be used to stimulate contractions of the womb and bring the process forward.
- Vacuum aspiration: where bleeding is heavy, where the body has not passed the sac by itself, or where waiting is causing distress the woman would rather not go through, the womb is emptied with fine cannulas in a matter of minutes.
Can you become pregnant again afterwards?
Having one anembryonic pregnancy does not mean that future pregnancies will end the same way. Most women recover physically after their first normal menstrual cycle, and the statistics show that the great majority go on to have a healthy pregnancy in a later attempt.
Every woman's body and every recovery is different. Do stay in touch with your own doctor, so that family planning and the follow-up that suits you can be worked out together.
This page is for information. It does not replace an examination or individual medical advice.